New methods of pest control in tea production.
World tea production has registered phenomenal growth, especially during the past four decades, from 621 million kg. in 1950 to 2,515 million kg. in 1990. Such a laudable increase has been brought about, to some extent, by an increase in new land areas coming into production, coupled significantly with improved technologies, including improved planting material, improved methods of plant husbandry, and new approaches to pest and disease control. These improved technologies have complemented each other by not only contributing their respective direct effects to crop improvement, but also by sustaining the positive impacts of the various other technologies on the rise in production.
The Economic Importance of Pest Control
New and modified pest control technologies, therefore, have played a very significant role in the management of tea cultivation in sustaining the improving trend in productivity at economic levels and, at the same time, maintaining the desired commercial quality, with good marketing potential.
If it had not been for the adoption of effective pest control measures, the serious pests attacking the tea crop in some of the major producing countries in south Asia would have affected the capital asset itself, causing a far greater loss and thus negating altogether the benefits of other improved agronomic technologies. Being heavily dependent upon export earnings from tea, such an unacceptable situation would have seriously affected the economy of these countries, with significant consequences on world supply.
Apart from the cost benefit analyses for specific pest control strategies, it is not possible to measure with any semblance of accuracy the beneficial impact of individual pest management technologies on the overall production cost. This is because, besides the direct contribution made by averting damage and salvaging the consequent crop loss, the actual benefits that accrue as a consequence of such crop protection are far greater because that protection helps to sustain the positive impacts of the various other production improvement technologies.
The earlier unilateral chemical approaches with broad-spectral persistent pesticides that dominated the tea pest control scenario in the 1960s and 1970s, although then seemingly highly cost effective, later proved to be the costliest approach in the long-term, in respect of the overall environmental dislocations and the necessary resuscitative treatments required to restabilize the tea growing environment. In this sense, the newer (modified) pest management technologies, based upon ecological approaches, have proved to be far more cost efficient by maintaining the target pest populations below the required economic damage threshold levels, within an undisturbed tea ecosystem. Furthermore, being mindful of the stringent market needs in a highly competitive international trade for this commodity, these newer (modified) approaches are geared toward ensuring minimal, if not zero, residual effects on the end product, assuring a cleaner product that has good market potential.
The newer chemical approaches are harnessed only in order to augment the efficacy of other control strategies, especially in specific situations when the latter are by themselves inadequate to maintain the target pest levels below the established damage threshold level. These chemicals are confined to the narrow spectral and less persistent, environmentally acceptable compounds, and are preferably limited to those with systemic properties. Microbial pesticides (commercialized formulations of infectious fungi, bacteria, and viruses) and plant-derived natural chemicals (botanicals) are presently playing an increasingly important role in chemical augmentation. The ongoing research efforts connected with such bio-pesticides have a greater role in the future tea pest management programs.
Modifying Agronomic Practices
Through a better understanding of the pest biology and its ecology, the modification of regular agronomic practices and the timing of their implementation, to either help sustain the target pest population below damage threshold levels, or enable the vulnerable growth stage of the tea bush to escape pest invasion, are gaining significance as important cultural strategies for improved tea pest management. Being regular agronomic practices, the harnessing of these cultural strategies is free of any specific additional costs.
The use of resistant and tolerant tea cultivars has shown excellent promise in the overall integrated pest management program of tea pests. In the past, the selection criteria for these tea cultivars centered mainly upon high yield and good cup character. Ironically, some of the selected high yielding cultivars turned out to be very susceptible to certain pests and diseases, thus compounding the problem further. As an important new pest management strategy, hybridization programs have been carried out to incorporate pest resistant characteristics. Because such classical breeding techniques require programs that are too long and drawn out, research attempts are presently aiming to develop genetically manipulated, gene-recombinant resistant varieties that can be rapidly multiplied through micropropagation (plant tissue culture). Gene-recombinant plants, besides having resistant characteristics, will also possess the genes for high yield and good cup character. This will undoubtedly be the ultimate goal of tea breeders and tea scientists.
The purposeful, manipulative biological control effected by harnessing the appropriate natural enemies, is presently gaining attention in many tea producing countries with varied success. Although one of the oldest, the reharnessing of this vital strategy - in light of a clearer understanding of the biology and ecology of the existing natural enemies - lends itself as one of the important elements to be integrated into a balanced ecological approach to tea pest management.
New Technologies & Approaches
Another environmentally acceptable approach for tea pest management that is yet to be perfected is to effect control of insects by causing disruptive changes in their normal metabolic processes with the aid of known natural products with metabolic disruptive properties. This new technology holds excellent promise for the future.
The labor component being of crucial significance in controlling costs of production in the tea industry, the appropriate man-day requirements, and the labor per unit of area are of great significance for judging its production efficiency and its effect on reducing costs. Unlike the manual harvesting of tea and other related field operations, labor requirements for pest control are generally low. Nonetheless, the development of technologies that require minimal labor needs has been of significance in improving cost efficiency.
The most cost-effective and environmentally acceptable procedure for managing tea pests, which would at the same time ensure the production of a clean, non-tainted product with good market acceptance, is to integrate the available newer technologies into a holistic management program (with each augmenting the other and with minimal dislocations to the environment) that will sustain the maintenance of the target pests below their respective economic threshold level.
Dr. P. Sivapalan has 34 years' experience in research and extension in crop protection and agronomy of plantation crops. For 12 years, he was head of the crop protection division of the Tea Research Institute of Sri Lanka and subsequently, from 1980 to 1994, was director of the Institute.